Measurement of surface fatigue damage by exoelectron emission

Abstract

Plastic deformation enhances the photoelectron emission from a metal-an effect known as exoelectron emission. Previous results demonstrated that fatigue cycling produces exoelectron emission from localized regions, and that by scanning the surface with a small spot of ultraviolet radiation these fatigued regions may be detected very early in life. This paper demonstrates that the intensity of the localized emission in steel is a true measure of the accumulated damage, and can be correlated with changes in the surface topography. The development of persistent slip bands produces microcracks in the surface oxide revealing bare metal from which the electrons are emitted. The growth of these bands and the formation and propagation of fatigue cracks increases the area of fresh metal surface and hence the emission. The increase in exoelectron emission is very systematic and hence provides a calibration for the prediction of the remaining fatigue life.